Proposal: remove arg server from buf processes

[elgiano]

I know this is a breaking interface change, but since it's impossible to have a buffer on one server and run the analysis on another, I think the server argument is redundant for all buffer processes. Such processes can get the server instance from the source buffer that gets passed to them:

// in, e.g. FluidBufMFCC.process
^this.new(src.server, nil, [features])
// instead of: ^this.new(server, nil,[features])

Since BufProcesses have already lots of args usually, I think that removing a redundant one would contribute to cleaner (e.g. more understandable/actionable) code